import java.util.*;

public class Main {
    public static int gcd(int a, int b) {
        while (b != 0) {
            int temp = b;
            b = a % b;
            a = temp;
        }
        return a;
    }

    public static int lcm(int a, int b) {
        return a / gcd(a, b) * b; // 防止溢出
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double ans = 0;
        int a = scanner.nextInt();
        int b = scanner.nextInt();
        int c = scanner.nextInt();
        for(int i = 1; i <= a; i++) {
            ans += i;
        }
        for(int i = 1; i <= b; i++) {
            ans += (i*i);
        }
        for(int i = 1; i <= c; i++) {
            double tmp = 1.0 / i;
            ans += tmp;
        }
        System.out.println(String.format("%.2f", ans));
    }
}
